Transitioning Lagrangian Particles to Mixture Multiphase (MMP)

In hybrid multiphase simulations that involve Lagrangian Multiphase (LMP) and Mixture Multiphase (MMP), if there are large numbers of small Lagrangian particles, for example aerosolized droplets (mist), it can be computationally more efficient to represent these particles as an MMP phase instead of tracking each LMP particle individually.

LMP particles are considered small when their diameter is significantly smaller than the cell size. During the transition, the accumulated volume, momentum, and energy of Lagrangian parcels are transferred to the MMP phase at each Lagrangian sub-time step.

You use the Subgrid Transition phase interaction model to identify the emerging particles and automatically transition them into equivalent mass MMP phase, determined by user-defined transition criteria.

You require a MMP Multiphase simulation with the Lagrangian Multiphase model activated.

To transition Lagrangian particles to an MMP phase:

  1. Define the transition MMP phase:
    1. Right-click the Multiphase > Phases node and create a new phase.
    2. For the new phase, Phases > [MMP phase], select the following models:
    Group Box Model
    Material One of:
    • Gas
    • Liquid
    • Multi-Component Gas
    • Multi-Component Liquid
  2. Define the Lagrangian phase:
    1. Right-click the Lagrangian Multiphase > Lagrangian Phases node and select New > Free-stream Phase.
    2. For the Lagrangian phase, Lagrangian Phases > [Lagrangian free-stream phase], select the following models:
    Group Box Model
    Particle Type Material Particles
    Material Select the same material as for the MMP phase. One of:
    • Gas
    • Liquid
    • Multi-Component Gas
    • Multi-Component Liquid
    Optional Models Two-Way Coupling

    See Lagrangian Phase Models.

The phase material in the Lagrangian phase should match that in the MMP phase.

  1. Create the MMP-Lagrangian phase interaction:
    1. Right-click the Multiphase Interaction > Phase Interactions node and select New > [ eulerian phase] > [Lagrangian phase].
    2. Right-click the [phase interaction] > Models node, in the Optional Models group box, activate Subgrid Transition.
    3. Select the Subgrid Transition > Lagrangian-Eulerian Transition Criteria > Particle Diameter Criterion node and set the Lower Bound Lagrangian Particle Diameter.
      Lagrangian parcels that have a diameter that is smaller than the specified value meet the criterion.
    4. Select the Subgrid Transition > Lagrangian-Eulerian Transition Criteria > Stokes Number Criterion node and set the following properties:
      Property Setting
      Critical Stokes Number Lagrangian parcels that have a Stokes number that is smaller than the specified value meet the transition criterion.
      Characteristic Length Specify a characteristic length scale that is used to calculate the Stokes number. The length scale can depend on your application.
      The Particle Diameter Criterion and Stokes Number Criterion are defined by default. If you do not require any of these transition criteria, you can delete the nodes.
    5. If you want to specify a user-defined criterion, right-click the Subgrid Transition > Lagrangian-Eulerian Transition Criteria node and select New User > Defined Criterion.
      You use a User Defined Criterion to set local Lagrangian parcel transition criteria.

    The Subgrid Transition Model determines which Lagrangian parcels transition to Eulerian blobs by checking the multiple criteria that you defined and transition takes place only for Lagrangian parcels that satisfy all the criteria. See Subgrid Transition Model Reference.

  2. (Optional). If you want to predict the particle size distribution in the MMP phase, choose the Discrete Quadrature S-Gamma model for the relevant MMP phase. See Discrete Quadrature S-Gamma Model Reference.
    注In cases where the S-Gamma model is selected, you create an MMP-MMP phase interaction, where one of the phase pairs is the one that is used in the subgrid Lagrangian-MMP transition.

    To increase the robustness of the simulation, when you are using the S-Gamma model, set the minimum volume fraction of the MMP phase to a value greater than zero for both the initial and boundary conditions.